The primary objective of this proposal is to evaluate the biochemical change in cardiovascular tissues of spontaneously hypertensive rat (SHR) which could alter the intracellular Ca 2 ion levels and thus provide the basis for increased vascular resistance and responsiveness seen in this model. The availability of Ca 2 ion in the vascular smooth muscle cell will be investigated at two levels (1) the factors which may influence the movement of Ca 2 ion across the plasma membrane and (2) the mechanisms modulating sequestration and release of Ca 2 ion by microsomes. In conjunction with the Na ion - Ca 2 ion exchange across plasma membrane (Na ion-K ion)-ATPase would be a critical determinant of intracellular Ca 2 ion. Our objectives include a detailed investigation of activity and kinetic properties of this enzyme in the cardiovascular tissues of SHR and WKY. Changes in the transition temperature(s) will be determined which could reflect alterations in the lipid composition of the membranes. Lipid composition will also be examined from cardiac and vascular smooth muscle membranes by TLC and GLC. The influence of phospholipids on (Na ion-K ion)-ATPase activity will be investigated through reconstitution studies employing partially purified enzyme into liposomes of known phospholipid composition and measuring the enzyme activity. Phosphorylation of the endogenous acceptor protein by the cyclic AMP-dependent protein kinase influenced Ca 2 ion sequestration by microsomes. To understand the molecular mechanisms which could result into reduced microsomal phosphorylation and Ca 2 ion sequestration by microsomes isolated from cardiovascular tissues of SHR, experiments have been designed to evaluate the differences in cardiovascular tissues of SHR and WKY in: (a) characteristics of endogeneous phosphate acceptor protein, (b) the activity and properties of cyclic AMP-dependent protein kinase isoenzymes and their ability to phosphorylate the endogenous membrane substrate, (c) the activity of phosphoprotein phosphatase, and (d) the activity of protein kinase inhibitor.